the radiochemistry of astatine.us aec

8/7/2019 the radiochemistry of astatine.US AEC

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Atomic I&iergy G,ommisE&orl ~:1r..Radiocbem@&y CM Astatine k:.!


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Iat iona lAcademyofSc iences vNat ional Researc h Counc ilBNUCLEAR SCIENCE SERIES

3_.

The Radioc hem is t ryof Ast at ine


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COMMITTEE ON NUCLEAR SCIENCEL.F.CURTIS43,hai?vnatz ROBLEY D.EVANS,ViceChz@zanNationalBureauofStandards MassachusettsnstitutefTechnology

J.A. I)eJUREN,SecretaryWestinghouselectricorporation

H.J.CURTISBrookhavenNationalaboratorySAMUEL EPSTEINCalifornianstitutefTechnologyHERBERT GOLDSTEINNuclearDevelopmentCorporationfAmericaH.J.GOMBERGUniversityfMichiganE.D. KLEMANorthwesternniversity

G.G.MANOVTracerlab,nc.W. WAYNE MEINKEUniversityfMichiganA.H.SNELLOakRidgeNationalaboratoryE.A. UEHLINGUniversityfWashingtonD.M. VAN PATTERBartolResearchFoundation

ROBERT L.PLATZMANArgonneNationalaboratory

LIAISON MEMBERSPAUL C.AEBERSOLD W. D.URRYAtomicEnergyCommission U.S.AirForceJ.HOWARD McMILLEN . WILLIAM E.WRIGHTNationalcienceFoundation OfficeofNavalResearch

SUBCOMMITTEE ON RAD!OCHEMISTRYW. WAYNE MEINKE, Chairman EARL HYDEUniversityfMichigan UniversityfCaliforniaBerkeley)NATHAN BALLOU HAROLD KIRBYNavyRadiologicalefenseLaboratory Mound LaboratoryGREGORY R.CHOPPIN GEORGE LEDDICOTTEFloridaStateUniversity Oak RidgeNationalaboratoryGEORGE A.COWAN ELLIS P.STEINBERGLos AlsmosScientificaboratory ArgonneNationalLaboratoryARTHUR W. FAIRHALL PETER C.STEVENSONUniversityf.ashington UniversityfCaliforniaLivermore)HARMON FINSTON LEO YAFFEBrookhavenNationalLaboratory McGillUniversity


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Radioc hem is try o f As ta t ineBy EVAN H. APPELMANArgo?vw National LaboratoryLemont, lllinoi-sMarch 1960 ,

Subcommitteeon Radtochemist~NationalAcademy ofSciencesNational Research Council

Printedh USA. Price$0.60 Availablerom theOfficeofTechoice.1Servlcea,epartmentofCommerce. Waabhgton26,D. C.


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FOREWORDThe Subcommittee on Radiochemiat~ is one of a number of sub-cammlttees working under the Committee on Nuclear Science ulthln theIiatlonalcademFof Sciences-NationalResearchCouncil. Itsmmdxxsrepresentgovernment,i.ndustial=d universitylabo=toriesin the areasof nuclear chemistry and analytical chemistry.The Subcommittee has concerned itself with those areas of nuclear

science which involve the chemist, such as the collection and distributionof mdiochemical procedures, the estabMshment of specifications for mdio -chemicaIly pure reagents, the problems of stockplllng uncontaminatedmaterials, the availability of cyclotron time for service irradiations, theplaceof radlochemistry in the undergmduate college program, etc.

This series of monogmphs has grown out of the need for up-to-date compilations of mdiochemlcal tifonnation and procedures. The 9ub-conmittee has endeavored to present a series which till be of maximum useto the working scientist and which contains the latest available hl%mm-tion. Each monograph collects h one volume the pertinent tifonnationrequired for ratiochemical work with an individual element or a gxoup ofclosely related elaents.

An expert hwritten the mmograph,committee. The Atomicthe series.

the radiochemlstry of the particular element hasfolloulng a standard format developed by the Sub-Energy Comlssion has sponsored the prtithg of

The Subcommittee is confident these publications will be usefulnot ODJ.Yto the radlochemlst but also to the research worker in other fieldssuch as physics, biochemistry or medicine who wlahes ta use radlochemicaltechniques to solve a specific problem.

W. Wayne Mdnke, ChairmanSubcouauittee on Radiochemiatry


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CONTENTSI.

11.III .rv.v.VI .VII.

General Reviews of Astatlne Chemi9tryand RadlochemlstryIsotopes of AstatlneHazards Involved in Handling AstatlneSummary of the Chemical Propert.tesof Astatlnepreparation of AstatlneTechniques for Counting Astatlne SamplesCollection of Detailed Procedures for Isolation andPurlflcatlon of Astatlne

A. Isolation of Astatlhe from TargetsB. Miscellaneous Radlochemical Methods

1122789921

28eferences


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INTRODUCTIONThis volume

astatine is one ofwhich deals with the radiochemistry ofa series of monographs on radiochemistryof the elements. There is included a review of the nuclearand chemical features of particular interest to the radio-

chemist, a discussion of problems of dissolution of a sampleand counting techniques, and finally, a collection of ra&io-chemical procedures for the element as found in theliterature.

The series of monographs will cover all elements forwhich rad.iochemicalprocedures are pertinent. Plans includerevision of the monograph periodically as new techniques andprocedures warrant. The reader is therefore encouraged tocall to the attention of the author any published or unpub-lished material on the radiochemistry of astatine which mightbe included in a revised version of the monographs.

vi


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The Radioc hem ist ry o f Ast at ine*EVAN H. APPELMAN

Argonne National LaboratoryLemont, Illinois

March 1960

I. General Reviews of Astatine Chemistry and Radiochemistry

Edward Anders, Ann. Rev. Nucl. Sci.~ 203 (1959).Earl K. Hyde, J. Chem. Ed. ~ 15 (1959).Earl K. Hyde, J. Phys. Chem. ~, 21 (1954)

II. Isotopes of AstatinelMass No. Half-life Principal modes of decay< 202 43 sec. electron capture, a


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80 q mlml@ aafdeciw208 I 1.6 hr. e. c.+o.5~a+7209 5.5 hr. 95* e. c., 5% a,~210 8.3 hr. electron capture + 0m2~ a + y211 7.2 hr. 5$ e. c., 41$ a212 0.22 sec. a213 ? a214 2X1O -6 ~~sec. a215 10-4 Bee. a216 3 x 10-4 Eec., a217 i).018sec. a218 2 sec. a + [email protected].. 0.9 min. 97$ a, 3$!3

111. Hazards Involved In Handling AstatineAll the precautions customsxy in the handling of

highly radioactive substances must be observed .Inworkwith astatlne. The tendency of astatine to concentrateIn the thyroid makes It particularly dangerous,

2and

ltevolatility makes it necessaryto provide adequateventilation during all operations. *t210 Is addition-ally hazardous because of its hard gamma ray and Its140-day, alpha-emlttlng P021Q daughter.

IV. SunInaryof the Chemical Properties ofAstatlne3-7Since astatlne has no long-lived Isotopes, chemical

studies of It must be conducted at very low concentra-tions--usually of the order of 10-15 ~. ThlsuAkes theastatine concentration comparable to that of the leastof the impurities In the experimental system. The re-


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action of the astatlne with such impurities often leadsto Irreproducible and unlntenpretable--not to say exce&l-Ingly frustrating--results which lend considerable un-certainty to our knowledge of the chemistry,of this element.

We might anticipate that astatlne, as the heaviesthalogen, would have properties roughly similar to thoseof Its lighter brethren. However, a close examinationof the chemistry of the halogens reveals marked differ-ences among them, and the radlochemist must at all timesbe acutely aw?xreof those properties which distinguishastatine from the other halogens.

At least four oxidation states of astatine have beenidentified in aqueous solutlon:

Astatlde, At-, 1s formedby reduction of higherstates with S02, zinc, As(III) at PH > 5, or ferrocyanldeat PH > 3 and Ionic strength < 0.1. It Is characterizedby nearly complete coprecipitation (>9C@ with AgI, TII,or Pb12.

The so-called At(O) Is the form In which astatineis usually found when left to Its own devices in acidicsolution. In the absence of macro quantities of otherhalogens, At(0) Is characterized by high volatility, atendency to be adsorbed on metal or glass surfaces, andby ready, but quantitatively unpredictable extractabilityfrom acidic aqueous solutions into organic solvents. !l?husIn a single extraction CC14, benzene, toluene,ene, n-heptane, or Isopropyl ether will remove~ of the astatine froman equal volume of ansolution.

cyclohex-from 70 toaqueous

Vsrlous workers have reported degrees of coprectplta-tlon of At(0) with insoluble iod~des and iodates ranging


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fran O to 90j%. The astatine may be nearly quantitativelyprecipitated with elemental tellurium formed in situ In.acid solutions, and will.partially precipitate with in-soluble sulfides and hydroxides.

The extractability of At(0) Into hydrocarbons orCC14 decreases markedly with the addition of halide ions,While the extractability into ethers is not greatlyaltered.

The,At(0) becomes unextractable into all organicsolvents when an acid aqueous solution Is rendered alkaline.The extractability Is usually largely restored if the solu-tion is reacldlfied wlthln a short time. From the alkallnesolution the astatlne Is completely copreclpitated with TIIor with AgI, the latter precipitated from an NH40H solution.

It has usually been assumed that the astatlne speciespresent in At(0) solutions is At2. The effeetof halideions might thenbe explained In terms of the formation ofsuch complexee a~ At21-, which would not extract Into CC14or.hydrocarbons, but might extract Into ethers as HAt21.,.The bexvlor in alkaline solution Is,explicable In termsof reversible hydrolysis to At- and HOAt.

However, as we have already noted, astatlne is subjectto reaction with impurities. At(0) should be especiallyvulnerable, Since not only is At2 expected to be extremelylabile In Its reactions, but any reaction which tends tobreak up the At2 molecule becomes thermodynamically favoredat these low astatlne concentrations. To make mattersworse, most of the experiments involving At(0) have beencarried out without adequate control of the oxidation po-tentials of the solutions. Thus in addition to At2 thesesolutions may contain assorted compounds of astatlne with


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whatever organic impurities happen to be around, the exactspecies present varying from one solutlon to the next. TtIs small wonder that irreproducible behavior has beenobserved.

These complications may be largely avoided If anotherhalogen and halide Ion are present at macroconcentratlons.Now not only does the macro X- --~ couple control theoxidation potential of the system, .but the.astatine is inthe form of a known Interhalogen compound, since there-actions At2 + X2 = 2AtX should be rapid and quantitative.Further, the maaro halogen will react preferentially withmany impurities which might otherwise reactwith the astatlne.

In the presence of iodine and Iodide the moderatelyextractable species AtI smd the unextractable complex ionAt$- appear to be formed. At 21C. the distrtbutilonbetween aqueous solutions and CC14 is represetitedW

D = organic astatine/aqueoua astatine = 5.5/1+2000(1-)

From fluchsolutions the astatine is not coprecipitated withAgI.or Pb(103)2. Addition of Tl+ to these solutions pre-cipitates TII-~ removing the Iodide, most of the ~, andall of the astatine from solution.. The 12 and astatiinemayreadily be removed from the precipitate by washln~:ltwithacetone. Pb12 does not coprecipltate astatine fromthesesolutLons If the stolchiometric 12 concentration is low;when it is high, both 12 and astatlne are partial.lyad-sorbed by the precipitate but may be removed by acetone.

In a system containing ~, =, and Br-, the astatlneis largely unextractable Into CC14, being present prlmar-Ily as the slightly extractable AtBr and the unextractableAtBr2-.


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The intermediate positive astatlne state or states,which we may designate At(X), have been identified prlmsr-ily on the basis of what they do not do. At(X) is com-pletely unextractable Into CC14 or benzene, though It mayextract Into ethers from several molar HC1 solutions, andit does not coprecipltate with Insoluble Iodi.desor Iodates.

At(X) is formed by oxidation of At(0) with Br2 or C12(but see followlng discus~ion of At03-) or by photochemicaloxidation with a VOH -- V02+ mixture or with Fe- atlow FeU concentrations. These photochemical oxidationsare reversed In the dark, returning the astatlne to theextractable At(0) state. The radlochemlst must alway6oonsider the possibility of Interference from such photo-chemical reactions.

Likely posslbilltles for At(X) are HOAt and HAt02,with the ether-extractable species being the correspondingpolyhalo-acids HAtC12 and HAtC14. However organoastatlnecompounds cannot be excluded from consideration.

Astatate, At03-, has been identified as an unextract-able qpecles completely copreclpitated with Ag103, Ba(103)2,or Pb(103)2. It Is formed by oxidation of lower astatinestates with Ce+4, hot persulfate, orhotperlodicacld.

+ is added to an 12t Is also formed when Ag --1- solutioncontaining AtI, presumably In accordance with the reactionAtI + 212 + 31-1# + 5Ag+ = At03- + 5AgI + 6H+. Althoughthe product of C12 oxidation of At(0) Is prlmarlly At(X),when no chloride is present In solution other than thatformed by hydrolysis of the chlorlne, partial copreclpi-tation of the astatlne with Pb(IO=)a is observed, and this>=may indicate partial oxidation of the

No evidence has been found for aAt(X) to At03-.peraBtatate.

6


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The following pdential diagram, referred to 0.1 M.acid, summarizes the oxidation-reduction behavior of asta-tine In acid solution. unknown At(o)At- -- -0.3 -- AtI -- -1.0 -- At(X)AtRr

At(X) -- -1.5 -- At03- -- < -1.6 --.H5At06

v. Preparation of AstatlneAstatine for chemical and mkdical studies and for

tracer use Is prepsred by bombardment of metallic bismuthor bismuth oxide with alpha particles of energy exceeding20 Mev, according to the reactions Bi209(u,xn) At213-x.The reactions with x = 2, 3, and 4 have threshold energiesof20, 28, and 34 Mev, respectively.8,9

Metallic bismuth, the more common target material, Iscustomarily fused or vaporized onto aluminum or gold ~ck-ing plates. Sihce astatlne may be volatilized from moltenbismuth it is necessay to cool the target carefuliy.Bismuth is a poor thermal conductor, and the cooling prob-lem Increases with the thickness of the bismuth layer. Theback of the target Is generally water-cooled. The face ismost effectively cooled by a flow of helium, though astatichelium atmosphere is often used. An 0.5 to 1 mil stainlesssteel or copper cover foil pressed tightly to the surfaceof the bismuth helps to dissipate the heat evolved and alsoprevents astatine from escaping from the target.

When bismuth oxide is used, it is generally pressedinto small holes drilled in the face of a thick alumlnumplate and thereafter treated in the same manner as themetallic targets. Melting of the target material Is muchless likely in this case.

7


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6clntlllator. It Is advantageous to reduce the relative-ly high background of *he sclntlllator by operating It asan energy analyzer reg18tering only counts of energy in thevicinity of the ca. 90 kv. k-x-ray of the astattnelHpolonium daughter.

*t211 decays in part to the long-lived Bi2W whichalso decays by electron capture. The ratio of initialAt211 x-ray activity to residual Bi2W activity is of theorder of 105. The bismuth is usually present In colloidalform probably adsorbed on duBt particles - and will becsxried along unpredictably through a surprisingly widevsrlety of chemical procedures. Only distillation of theastatine can be reliei on to-remove all of the Bi2W.Samples x-ray assayed for astatlne some time after purifl-

2W should be recounted after the astatineation from Bihas entirely decayed away, the resulting B1207 count beingsubtracted from the original count of the sample.

The techniques outlined here for At211 apply gener-ally to the other astatine isotopes, with specific mdifl-catlons srislng from the decay scheme of the partlcula-isotope in question. Thus, for example, At210 may alsobe assayed by scintillation counting of its 0.25 and 1.2Mev gamm rays.

VII. Collection of Detailed Procedures for Isolationand Purification of Astatlne

A. Isolation of Astati.nefrom TargetsMethods of two types are available for remoting asta-

tlrlefrom bismuth targets--those involving distillationof the astatine from the umlten tsrget and those Involving


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PROCEDURE 1DISTILLATION OF ASTATINE FROM MOLTEN BISMUTH IN A~10

For very rapid separation of astatine from the blstithtarget, a-method Is used which gives astatine of somewhatuncertain purity but which is considered adequate for de-termination of short-lived alpha-emitters. The basis forthe method is the distillation of astatlne from moltenbismuth. The bismuth target is dropped into a stainlesssteel crucible fitted on top with a water-cooled steelfinger to which a collecting platinum disk is clamped.When the bismuth Is kept slightly above its melting point(as measured by a thermocouple fitted into swell in thecrucible),,within a few seconds astatine distills onto thecollecting plate. Polonium does not distill in appreciablequantities until considerably higher temperatures arereached. Using a vacuum csrrier system to deliver thetarget, this prooedure permits samples to be in the alpha-puise analyzer within 90 seconds after the cyclotron beamiS shut off.

Editors Comments: This method was confirmed by the editorand Ralph D. McLaughlin.7 Although the astatine begins tocome off the target at the melting point of the bismuth,temperatures as high as 8000C. may be required to effectnearly quantitative removal. Astat@e collected at suchtemperatures will be contaminated with anypolonium whichmay have been present in the target, and also with some bis-muth . The adherence of the astatine to the collecting plateis strongly dependent on the material of which the plate ismade. Deposits on platinum or silver are strongly adherent,while those on aluminum are much less so.11


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~.1 (Ccmtd.This procedure has also been found suitable for iso-

lating astatine prepared byheavy-lon bombardment of gold.In this case the gold Is dissolved in the molten bismuth.12

PROCEDURE 2PURIFICATION OF ASTATINZ ISOIATED BY PROCEDURE 17The astatine-containing plate from Procedure 1 Is

placed in a tube on the end of an all-glass vacuum systemincorporating a U tube.a he plate is heated to 120C. withan electrlc furnace to drive off volatile impurities. Allquld nitrogen cooling bath 16 placed around the U tubeband the furnace temperature Is raised to 500C. over about10 min.= The vacuum Is broken and water or any des~edaqueous solution Is added to the cold U tube. Upon thawing,the solution Is withdrawn, leaving virtually none of theastatlne behind. Yields are in the vlclnlty of 5*.Notes:

aSeveral centimeters of glass tubing between-the U tibeand the platinum plate Is desirable to prevent poloniumfrom transferring to the Utube. If po~otiiumcontaminationIs not a problem, this tubing may be heated to 100C. ormore during the distillation to prevent adsorption of @sta-tine on the glass. Hydrocarbon @eases should be avoidedbetween the U tube and the plate,since they have a strongtendency to adsorb astatlne. Dow Corning silicone greaseadsorbs relatively llttle aBtatlne, as does a totallyfluorinated fluorocarbon fraction (e.g. Hooker ChemioalCompany Fluorolube HG 1200).bA bath at dry-ice temperature may be used, but In this


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~ 2 (Centd.case a portion of the astatine may pass through the trap.

CA furnace Is better for this heating than an inductionheater, nlnce when the latter $.sused the astatine has atendency to leave the hot metal plate aod become irre-trievably Imbedded In the cooler glass walls of the tube.The temperature of the furnace should be raised gradually.

PROCEDURE 3DISTILLATION OF ASTAT~ FROM ~LTEN BISMUTH

IN HIGH VACUUM4The procedure used was to dlstlll the astatlne from

bismuth at its melting point In an all-glass system, andcollect the carrier-free element in a four-millimeterdiameter U tube cooled by llquid nitrogen. The U tubewhile sttll cold was washed with one drop of concentratednitrfc acid, allowed to stand 1 hour, and then washed withdlstllled water Into a stock bottle. & this method three-milliliter solutions were prepared containing 0.5-molarnltrlc acid and 107 dlelntegratlons/sec. of astatlnem sucha solutlon is 2.1 x 10-lo molar with respect to aet.atine.Yields up to 0.95 were obtained with legs than 0.001 ofany polonium present In the original target coming over.

Astatine evaporated on glass Is very poorly held bythis gurface at room temperature. Based on this informa-tion, a double separation of astatine from bismuth andpolonlum was accomplished. A bismuth plate was bombardedin such a way as to accumulate In It approximately equalnumbers of polonium and astatlne atoms, after which afirst distillation was carried out In the usual way. Thetube containing the bismuth was sealed off and the astatlne


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~3 (Centd.)then d16tllled at room temperature to a second U tubecooled by liquid nitrogen. The yield of this experimentwaa 0.83 of the aBtatine present on the original tsrget,with less than 10-6 of the polonium coming over.

Editors Comments: This procedure IB preflentedon a caveat- baBis The editor and Ralph D. McLaughlin testedthe method but were unable to repeat It successfully.7 Inour experiments the astatlne dld not distill below 600c.Above this temperature the bismuth Itself began to distill,carrying the astatlne with It. Johnson, Lelnlnger, andSegrebombarded bismuth layers less than 40 mg/cm2 thick on1 mll aluminum backings. Our bismuth layers were from 0.5to 1 g/cm2 thick on 10 mll alumlnum backings. It IS pOS-slble that the difference in thickness of the bismuth IsIn some way respofislblefor the difference In results.

We also had dlfflc.ultyredlstllllng the astatlne fromglass. It was often necessary to heat the glass to severalhundred degrees centigrade before the astatlne was removed.The astatine was probably being held by Impurities whichcondensed with it. Adark stain was often visible at thepoint on the glass where the astatlne had aondensed.

PROCEDURE 4DISTILLATION OF ASTAT~ FROM MOLTEN BISMUTH

IN A STREAM OF INERT GAS13About 220 mg/cm2 of spectroscopically pure bismuth are

fused to a 10-mll gold disc, 3-3/8 inches in diameter, toconform to the 2-by-7-cm. collimating slot in the cyclotronwindow assembly, Fig. 1. The beam Is sufflctently well

u


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~4 (Centd.collimated so that with centering of the bismuth more than8c73 of the gold target may be recovered free ofInducedradlotictlvitles. Enough platinum foil Is placed In the pathof the alpha beam at A (Fig. 1) to degrade the alpha-p&i-cle energy to 29 Mev. This is the optimum energy for the51pha-2n reaction with bismuth to form At211 without simul-taneously producing At210 by the alpha-3n reaction.

Air Is blown In along the side of the platinum foilsto dissipate the heat produced by the be&m. One-halfatmosphere of helium Is held In the area between the foilsand.the bismuth so that this areawlll be free of any oxy-gen. The-presence of oxygen would lead to the formationof bismuth oxide,.which could be carried over In the sub- .sequent diatlllatlon operation. Because At211 is veryvolatlle,even at room temperatures, water cooling Iscarried on just behind the gold target plate at B (Fig.1).The total beam on the assembly In microampere hours is in-dicated by the Integrator (Fig. 1~. ,

At the end of the bombardment, the target and holderare allowedto cool for a short period of time to permitthe decay of the short-lived radioisotopes produced Inthe aluminum, platinum, and gold foils. The target plateIs then remved from the assembly and carefully dried.After the removal of the excess gold from either side ofthe gold-bismuth alloy, the target Is cut lengthwise Intotwo pieces, taking care to avoid flaking of the bismuth.These two pieces are placed In a smll quartz boat, whichIs Inserted Into the large quartz tube shown at C (Fig. 2).Survey-meter readings we taken at the surface of theheating unit and at the cold finger D (Fig. 2) in order to

14


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VACU

ROGEN

FIGURE 2.


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~k (Ccmtd.)provide a reference pint for later determination ofcompleteness of the dlstlllatlon of the At211. Llquld ni-trogen Is put In the cold finger reservoir F (Fig. 2) andaround the trap E (Fig. 2). In order to faollltate col-lection and to prevent the adsorption of the astatlne onthe glass of the cold finger, a thin film of Ice isdeposited on the finger by soft breathing. The entiresystem Is evacuated with a Cenco-Megavac pump and testedwith a Tesla coil. When a vacuum of less than 200 mi-crons is obtained, an inert streaming .gas--helium or nl-trogen--1s introduced through the capillary tube betweenA and B (Fig. 2). ~o pounds Of pressure Is maintainedon the tank side In order to permit a steady flow of gasover the blsmutlito the cold finger. Neither water noroxygen Ie permitted to enter the system, because it hasbeen found that these tend to Increase colloid formation.

The furnace Is turned on, and the target is broughtrapidly to 700C as determined by a thermometer $nsertedh B (Fig. 2): Below this temperature the yield of At211Is low and above It a brown to black layer of bismuth maydlstlll onto the cold finger and cause great los~ ofactivity In subsequent centrlfugatlon. The quartz tubebetween the furnace and the finger Is flamed periodicallyto prevent adsorptl.onof any activity on the wal16 of thequartz tube. The temperature Is held at 700C.for approx~-mately 40 minutes, or until survey-titer read~ngs give nofurther indicatl.onofmovement of activity from terget tofinger.

The furnace is turhedatus is allowed to cool to

off and opened, and the ap~-approximately 100C. The vacuum


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4 (Centd.pump IS turned off. When the system has returned to at-mospheric pressure, the cold finger is carefully lifted straightup to prevent any of the Ice from flaking off. The finger Iswashed with 10 ml of isotonic saline containing 5 mg/ ml ofNa@03 . This solution Is placed In an ultracentrlfuge for20 minutes at 30,000 rpm. The centrifuge oone is read witha survey meter and the value recorded. The supernatant Istransferred to a 25=ml serum bottle. A 10-ml volume of wateris added to the cone and shaken with the residue. The coneIS again metered to determine the amount of activity remain-ing in the cone as colloid.

Editors comments: The editor uonfirmed this procedure, ob-tainingsimilarof Hg.

yields of about l%. Garrison et al.14 geport aprocedure using a flow of nitrogen at 10-2 to 10-3 mm.They heated the bismuth only to 425C.

mocEmFfE 5ISOLATION OF ASTATINE EY DISSOLUTION OF THETARGET AND EXTRACTION INIUISOPROPYL ETHER5

(See also Procedure 6)In making the isolation from the target, the bismuth is

dissolved In nitric acid and the solution concentrated byboiling. The solution is not taken to dryness, as a littleHN03 does not interfere. Concentrated HC1 is added to bringthe HC1 concentration to 8 g andextracted with Isopropyl ether.a

previously been equilibrated withthan pure ether for this purpose,

the solution is cooled andIsopropyl ether that has8 ~HCl is somewhat betterslnoe its use minimizes

volume changes. The yields In a single extraction exe betterthan 9@, the presence of Bi(III) salts increasing the extract-


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~5 (-tdo)ability. Washing the ether phase with 8l@ of the aotlvlty. Less than O.Olj%ofretained In this prooeaure.

In the reoovery of astatineoxldatlon states of astatlne exeacid, lower oxldatlon states are

~HCl removes aboutthe bismuth Is

from residues, higherreduoed with hydrochloricoxidized with C12. Or-

ganic forms are apparently not affected by thisBecause of the large amount of sodium compoundsappeared in the residues, sodium chloride often

treatment.thatprecipi-

tated from the 8 ~HCl solutions. Separation by oentrifu-\gation is satisfactory, asthere Is no tendenc$yfor thecomplex to be retained on the precipitate. Iron salts, Ifpresent, are oxldlzkd to Fe(III) and areextracted alongwith the astatlne. Back-extraction with NaOH solution pre-cipitates Fe(OH)3, which will oarry some of the astatlne.Only about 5@ of the astatlne Is oarrled If the amount orFe(OH)3 Is not exorbitant. The extraction prooedure alsoserves to separate from Po210 , which acw.mmlates from thedecay of At210.Note:

%!heIsopropyl ether has previously been purified fromperoxides by washing with three portions of saturatedaqueouE FeS04, followed by three portions of water.

Editors comnents: The editor has oonflrmedithls =thodwith certain exceptions: The HC1 used to wash the astatine-containlng ether should be about 1 ~ In HN03. If.no ni-trate is present up to half of the astatlne activity may bebackextracted In this wash. Neumannastatlne with 0.5 M NaOH. However I

backextracted thehave found the complete-


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~ 5 (CmLt,d. )nesB of thi~ back-extraction to be vexlable. Sometimes lessthan half of the astatlne can be backextracted. I have nottested the use of this method for the recovery of astatlnefrom residues.

mocmum 6ISOLATION OF ASTATINE BY DISSOLUTION OF THE

TARGET AND EXTRACTION llTl?OSOPROPYLETHER,AND PURIFICATION FROM LEAD,BISMUTH, AND POIONIUMIO

The method developed for removal of pure astatlne con-sisted In its extraction, presumably while In the zero oxi-dation state, into diisopropyl ether (DIPE). The bismuthtarget was dissolved in such a manner as to end up with asolution In concentrated hydrochloric acid to which ferroussulfate was added to make sure that the astatine was re-duced to the zero state= This solution was contacted withDIPE. The DIPE solution was washed with dilute sulfuricacid, or hydrochloric acid, and so fax as could be told byabsence of polonium and bismuth alpha-aotlvity, the asta-tine was pure. Samples of the DIPE solution could then beevaporated on platinum or stainless steel disks for radia-tion measurement.

A solution containing pure astatine isotopes begins togrow, successively, polonium and lower element daughtersprincipally by electron capture decay. The polonium, bis-muth, and lead may be removed periodically by adding one-tenth volume of 20 percent tributyl phosphate (TBP) inisobutyl ether to the DIPE solution and extracting intoa 2M nitric acid--4~ hydrochloric acid aqueous solution.Theee elements leave the crganic phase, quantitatively,


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~6 (Centd.)In only about one ml,nutecontact time while the aOtatlneremains quantitatively In the organic layer. The polo-nium cti then be seperated from bismuth and lead by ex-tracting Into TBP solution after destroying the nitrateIon and making the aqueous solution ,6~HC1. The bismuthand lead sre separated by precipitating the bismuth asBIOC1 end the lead as PbS04.

PROCEDURE 7ISOLATION OF ASTAT~ FROM BISMUTH OXIDE TARGEPS15The targets consisted of pockets of Bi203 Imbedded

in the surface of an aluminum slab. Uter Irradlatlonthe BI.203was dissolved in HC104 containing a littleiodine, and the bismuth was precipitated as the phosphate.B. Miscellaneous Radlochemlcal Methods

PROCEDURE 8DETERMINATION OF ASTATINE IN BIOLOGICAL MATERIAIS

BY COIIIECIPITATIONWITH TELLURII.JM14A sample of astatine-containing tissue (less than 10

grams wet weight) Is plaoed in a 100-ml. borosllicate glassbeaker and digested in a minimum volume of 9 N perchlorlcacid containing 30$%by volume of 16 ~ nitric acid. Afterthe organic material has been oxidized, the clear solutionis evaporated to 10 to 15 ml. of concentrated perchlorlcacid. The solution Is cooled and diluted to 3 ~and 5 mg.of tellurium as tellurous acid are added together with 1 ml.of 12 ~ hydrochloric acid. (Tellurous acid Is only slowlyreduced in cold 3 N perchloric acid In the absence ofdilute hydrochloric acid) A stream ofsulfur dioxide ispassed through the solution, precipitating metallic tellu-


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~e (Centd.)rlum which carries astatlne quantitatively.is seperated by centrlfugation, washed three

The telluriumtimes with

distilled water, and transferred to a porcelalncountingdish. After drying at 70C., the dish Is counted foralpha-actlvlty.

Editors conmnent: According to Corson, MacKenzie, andSegre~ any polonium present remains quantitatively Insolution when tellurium is precipitated In this way, andthe astatlne may subsequently be freed fromtellurlum byprecipitating the latter from alkaline solution withsodium stannite.3

I?Rocmxlm 9DETERMINATION OF ASTATINE IN BIOLOG;~AL

MATKRIAL9 BY DEPOSITION ON SIL~A sample of astatine-containing tissue is digested

in a mtiture of perchloric-nitric acid.a After digestionis complete, the solution is evaporated until the perchloricacid fumes (approximately 10 ml.), diluted to 3 ~withthe addition of distilled water, smd transferred to a50-ml. beaker. A circular silver foil 2 roilsthick of asize convenient for alpha counting is placed in the bottomof the beaker and the solution is stirred for 30 minutes.The foil is washed in water and acetone, dried in air, andcounted for alpha-activity. Although the astatine de-posits principally on the top surface of the silver foil,for quantitative results both sides of the foil should becounted for alpha-activity.Note:

aThe digestion procedure is that detailed in Procedure 8.22


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~9 (Centd.)Editors comments:tested this method

The editor and Ralph D. McLaughlinbut were unable to obtain reproducible

results with It. In some experiments the astatine wasquantitatively removed from solution, while in others, lessthan half of it could be renmved. The method does notprovide a sep~ation from polonium, which Is also deposi-ted to a large extent on silver foils.

PROCEDURE 101627 ~131 ~ &ll IN TBSIJECODETERMINATION OF I ,

l?heapparatus oonslsted of a one-liter Claisen flaskfitted by a ground-glass joint to a thistle tube with astopoock and by a second joint to an all-glass water-jacketcondenser with a delivery tube bent nearly to a right angle.Erlenmeyer flasks one-third full of CC14 and surrounded byan Ice bath served aa receivers. The reoelvlng flaskswere placed so that the dellvery tube dipped well belowthe surface of the CC14.

The th~ld glands were weighed, and no more than 50grams was employed in a single determination. Thyroidglands weighing more than 50 grams were divided Intoapproximately equal portions which were assayed separate-ly. The tissue sample and some glass beads were placedin the flask with approximately three times the tissueweight of chromium trloxide. The neck of the flask waswashed with three times the tissue weight ofwater. Afterthe initial bubbling hadlC acid equal to that ofthe thistle tube. Since

subsided, a volume of 36 ~ sulfur-the water was added slowly throughthe reducing capacityof blologi-


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cal materials Is variable, it was sometimes necessary touse more than the stated amounts of reagents. The colorof the reaction mixture usually was Indlcatlve of the pro-gress of the oxidation. Persistence of the dark-greenchromic Ion indicated that the oxldatlon was not completeand more chromium trloxlde, water, and sulfuric acid wereadded. All the reagents used were C.P. grade.

When the addition of the acid was complete, and theviolent reaction had ceased, the flask was heated slowly toa boil, and water was distilled until the amount of water

/ collected In the receiving flask was nearly equal to that,,.originally added, or until excess chromium tri.oxidepre-cipitated. A smll amount of distilled water (10 to 20 ml)was added and the distillation was continued for a fewminutes to Insure the complete removal of chlortie and towash out the con~enOer. Over-heating was avoided becauseof the possibility of carrying spattered dlchromate overinto the con-denser.

The reaction flask was then allowed to cool to about50C, and the receiver wasreplaced by a 500-ml Erlen-meyer flask contaln~ng 200 ml Of fresh CC14. Neither theAt211 nor 1131 wa~ found In measurable quantities In theinitial aqueous or organic phases in the ffrst receivingflask.

From 50 to 200 grams of oxalic acld,a depending onthe amount of tissue In the sample, =e added slowly, afew cryfltalsat a time until the evolutlon of C02 ceasedand the solution was dark green In color. The flask wasthen heated and water, iodine,distilled,over until the brown

and some of the At211 wereiodine color was no longer


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~ 10 (Centd.dlacernable In the delivery tube. The distillation waacontinued until another 20 to .30 ml of water had beencollected.

After the flask had cooled nearly to room temperature,three times the tissue weight of a@@rous ferrou~ sulfatewas added, and the neck of the flask was washed with 20 mlof water. The distillation was continued, using the samerecelvlng flask= until ferrous mlfate precipitated In thebottom of the distilling flask as a greenish-white solid.The distillate and the CC14 were transferred to a lmgeseparator funnel with enough 0.2~ Na@03 to completelyreduce the iodine. The layers were separated and the CC14was discarded. The volume of the aqueous layer was re-corded, and duplicate allquots for radioactive assaywere plpetted Into olean tinned bottle caps.b: One ml of0.2~KI In 0.1 ~NaOH and an excess of 0.1 ~AgN03 wereadded. The samples were mixed by carefully rotating thecaps and were dried slowly under a heat lamp at 75C.The sampling technique described above Is quantitative,presumably as a result of the efficient scavenging of theastatine by the mixed AgI-~0 precipitate, whlch~ onhetitingIn contact with the tinned mount, Is reduced toform a thin unlformfilm of metallic silver completelybinding the astatlne.. The samples w@re assayed forAt211 alpha activity In an ionization chamber, and for1131 gamma activity wit,ha ~c%ntlllatlon counter,,c

The stable-iodine content of the,samples was deter-mlnedby oxidizing an aliquot of the iodine-containingdistillate with diluteinto a known volume of

HC1 and ~02 and re-extractingCC14. The concentration of 12


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mccEmm 10 (Centd.In the CC14 was measured with a previouslyEeckman spectrophotometer at a wave length

calibratedof570 m.

The accuracy of this method was checked by pilotexperiments using samples of rat muscle or beef thyroidto which hadbeen added known amounts of At211 and 1131.The recovery of the At211 was 90.2 ? 2.8$ and that of1131 was 98 k 1$.

The recovery of iodine, both stable and radioactive,was quantitative after the reduction with oxallc acid andthe subsequent distillation aa 12. When the pilot experim-ents were performed, It was anticipated that At211 wouldbe recovered quantitatively in the CC14 phase followingthe reduction with oxallc acid, as was iodine. It wasfound, however, that the reoovery of the At211 was erraticso that the subsequent reduction with ferrous sulfate wasIncluded In the method to Insure the accuracy of the deter-rnlnatlonof At211.Notes:

%heuse oflarge crystals of oxalic acid Is recormnended,especially in the early stages of the reaction, which isquite violent.

bWhen these bottle caps are received from the dealer,they are coated with a thin film of laoquer. This Is re-moved by soaking for a tew hours in 6 ~ NaOH warmed on ahot plate.

cThe scintillation counting was done through 0.5q/cm2of lead to remove a and P particles and At211 x-rays.


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PROCEDURE 11DETERMINATION OF fLSTATINEBY COPRECIPITATION

WITH METALLIC SILVER OR PAIJ.ADIU?#Silver or palladium Ion Is added to the astatine solu-

tion. Then sufficient sodium sulfite Is added to precipi-tate aii of the added cation as the metal. If a nlDrlcacid soi-utlonIs used, enough Bulflte must be added tonearly completely neutralize the free acid. Iess than0.5$ of the astatlne re=lns In solutlon.


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REFERENCES

1.

2.

3.

4.

5.5.

7.

8.9.

10.

D. Strominger, J. M. Hollander, and G. T. Seaborg,Rev. Modern Phys. 30, 585 (1958).J. Hamilton, C. Asling, N. Garrison, and K. Scott,The Accumulation, Metabolism, and Biological Effectsof Astatine in Rats and Monkeys,tUniv. Calif. Publ.Pharmacol. 2_,283-343 (1953).D. Corson, K. MacKenzie and E. Segre~ Phys. Rev. 58,672 (194o).G. Johnson, R. Leininger, and E. Segre% J. Chem. Phys.17, 1 (1949)..H. M. Neumann, J. Inorg. Nucl. Chem. ~, 349 (1957).H. M. Neumann, Solvent Distribution Behavior of aPositive Oxidation State of Astatine. Paper presen-ted at the 133rd meeting of the American ChemicalSociety, April 1958. Division of Inorganic Chemistry,Abstract No. 84.Evan H. Appelman, Chemical Properties of AstatineUCRL-9025 (196o) (Thesis).E. Kelly and E. SegreflPhys. Rev. 75, 999 (1949).Walter John, Jr., Phys. Rev. 103, 704 (1956).G. Barton, A. Ghiorso, and I. Perlman, Phys. Rev. 82_,13 (1951).

11. Paul Donovan, private communication, (1959).


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12. W. E. Burcham, Proc. Phys. Sot. (London) 67A, 555 (1954).13. M. Parrott, W. Garrison, P. Durbln, M. Johnston,

H. Powell, and J. Hamilton, The production andIsolation of Astatlne-211 for Biological StudiesUCRL-3065 (1955).

14. W. Garrison, J. (llle,R. Mexwell, and J. Hamilton,Anal. Chem. 23, 204 (1951).

15. A. Aten, T. Doorgeest, U. Hollsteln, and H. Moeken,Analyst ~ 774 (1952).

16. P. Durbln, J. Hamilton, and M. Parrott, The Co-determinatlon of Iodine-127, Iodine-131, and Aata-tine-211 In Tissue, UCRL-2792 (1954).

.,,,


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MC .15 I::(I

the radiochemistry of astatine.us aec

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